Injection mold and molding method for resin molding

Abstract

Molten resin supplied from a sprue to a runner in a mold closed state flows substantially radially in the runner and then flows from an entire circumferential edge portion of the runner into a cavity via a film gate. When the molten resin is filled in the cavity and molding is completed, the core part is slid while keeping the mold closed state to thereby cut a thin portion formed in the film gate in a manner of pulling the runner part by Z pins. After gate cutting, when the movable mold is opened with respect to the fixed mold, the resin molding (ring-shaped part) formed in the cavity is taken out.

1 . An injection mold, comprising:
 a sprue to be an inflow path for molten resin;   a disk-shaped runner communicating at a center thereof with the sprue;   a cavity arranged along an outer peripheral portion of the disk-shaped runner; and   a film gate through which molten resin flows from an entire circumferential edge portion of the disk-shaped runner into the cavity.   
   
   
       2 . The injection mold according to  claim 1 , wherein
 a circumferential edge portion of the disk-shaped runner is thicker than a center portion thereof.   
   
   
       3 . The injection mold according to  claim 1 , further comprising:
 a fixed mold;   a movable mold; and   a core part provided to be relatively movable with respect to the movable mold,   wherein a Z pin holding a runner part formed in the disk-shaped runner is provided in the core part, and   wherein while the fixed mold and the movable mold are in a mold closed state, moving the core part causes the Z pin to move and thereby causes a thin portion formed in the film gate to be cut.   
   
   
       4 . The injection mold according to  claim 2 , further comprising:
 a fixed mold;   a movable mold; and   a core part provided to be relatively movable with respect to the movable mold,   wherein a Z pin holding a runner part formed in the disk-shaped runner is provided in the core part, and   wherein while the fixed mold and the movable mold are in a mold closed state, moving the core part causes the Z pin to move and thereby causes a thin portion formed in the film gate to be cut.   
   
   
       5 . The injection mold according to  claim 3 , wherein
 when the disk-shaped runner has a diameter larger than 30 millimeters, the Z pin is arranged separately at a distance equal to or greater than 15 millimeters from the cavity.   
   
   
       6 . The injection mold according to  claim 4 , wherein
 when the disk-shaped runner has a diameter larger than 30 millimeters, the Z pin is arranged separately at a distance equal to or greater than 15 millimeters from the cavity.   
   
   
       7 . The injection mold according to  claim 5 , wherein
 a plurality of Z pins identical to the Z pin are arranged symmetrically.   
   
   
       8 . The injection mold according to  claim 6 , wherein
 a plurality of Z pins identical to the Z pin are arranged symmetrically.   
   
   
       9 . The injection mold according to  claim 3 , wherein
 when the disk-shaped runner has a diameter of 30 millimeters or smaller, the Z pin is arranged in a center of the disk-shaped runner.   
   
   
       10 . The injection mold according to  claim 4 , wherein
 when the disk-shaped runner has a diameter of  30  millimeters or smaller, the Z pin is arranged in a center of the disk-shaped runner.   
   
   
       11 . The injection mold according to  claim 3 , wherein
 the Z pin is replaceable with another pin.   
   
   
       12 . A molding method for a resin molding, the method comprising
 molding a resin molding having a hole using an injection mold, wherein the injection mold comprises:   a sprue to be an inflow path for molten resin;   a disk-shaped runner communicating at a center thereof with the sprue;   a cavity arranged along an outer peripheral portion of the disk-shaped runner; and   a film gate through which molten resin flows from an entire circumferential edge portion of the disk-shaped runner into the cavity.